The present invention relates to storage-stable one-component dispersions comprising surface-deactivated isocyanates and isocyanate-reactive polymers, and to their preparation as well as to their use.
Nowadays, high-performance adhesive bondings are achieved according to the state of the art using reactive adhesives. A number of different adhesive systems are known for this purpose. Polyisocyanates are used for many applications in this field due to their high reactivity.
Depending on their respective application, a distinction is made between so-called two-component adhesive systems and one-component adhesive systems.
Two-component systems are mixed directly before application, wherein this requires an additional step for the user. In addition, dosage or mixing errors may occur during mixing of the two components.
In addition, there are one-component adhesive systems, such as, for example, isocyanate-terminated polymers which cross-link, after being applied, by reacting with moisture. The disadvantage with these systems is that hardening takes a long time since cross-linking depends on the rate of diffusion of the water. With very thick layers the cross-linking may also remain incomplete.
Stable one-component systems with chemically blocked isocyanates are also known which can be formulated by chemical blocking of the isocyanates with monofunctional reaction partners (e.g. EP 159 117). This blocking is thermally reversible so that under the effect of heat, the blocking agent is separated and the released isocyanate forms a thermostable bond with the reactive groups of the polymer by cross-linking. A disadvantage with these systems is that if the blocking agent is volatile at the temperatures of application, it vaporizes and may thus affect the environment or, if it remains in the adhesive, it may lead to degradation or deterioration with respect to the quality of the adhesive bond. In addition, such a system is not suitable for thermally sensitive substrates because the blocking agent must be separated under the effect of heat.
EP 0 204 970 A2 and U.S. Pat. No. 4,888,124 belonging to the same patent family disclose a method for producing stable dispersions of surface-deactivated or encapsulated solid polyisocyanates in a liquid by treatment of polyisocyanates with suitable deactivating agents. In order to disperse polyisocyanates, particularly solid polyisocyanates, so that they are storage-stable, and in order to prevent any premature, undesirable reaction with the medium, the dispersed isocyanates are deactivated at their surface with a suitable deactivating agent. The polyisocyanates are thus stabilized by applying a polymer shell to the surface of the polyisocyanate. The isocyanates treated in this way then have a so-called retarded reactivity. They are described synonymously as xe2x80x9cencapsulated isocyanatesxe2x80x9d, xe2x80x9csurface-deactivated isocyanatesxe2x80x9d or only as xe2x80x9cdeactivated isocyanatesxe2x80x9d.
The afore-mentioned patents EP 0 204 970 A2 and U.S. Pat. No. 4,888,124 also disclose the use of said dispersions of surface-deactivated solid polyisocyanates produced as cross-linking agents according to the method in these documents.
A disadvantage with the systems described in EP 0 204 970 A2 and U.S. Pat. No. 4,888,124 is that the breaking-up of the deactivating polymer shells, particularly polyurea capsules and thus the cross-linking reaction starts at temperatures between 70 and 180xc2x0 C. Thus, such systems are not suitable for thermally sensitive substrates.
EP 0 505 889 A2 describes aqueous suspensions of encapsulated or surface-deactivated polyisocyanates in quantities of at least 12 wt. %, relative to the NCO content of the dispersion, wherein the encapsulation or surface deactivation of the polyisocyanate is brought about by allowing the dispersed polyisocyanates to react with polyamines having molecular weights below 400 in an equivalent ratio of amino groups to isocyanate groups (NNH2/NNCO) of at least 0.05:1.0, i.e. at least 5%. The dispersions described have a longer pot-life, but are not storage-stable since, as the Examples show, the isocyanate content decreases significantly after a few hours. The dispersions described are thus not suitable for being processed into films since they comprise no isocyanate-reactive components.
EP 0 922 720 A1 and the international patent application WO 99/29755 describe a method for producing storage-stable latent-reactive layers or powders of surface-deactivated solid polyisocyanates and isocyanate-reactive polymers with functional groups. The polyisocyanates in the Examples are deactivated with polyamines having high molecular weights. A disadvantage of the dispersions described is that they start to cross-link at higher temperatures so that they are not considered for methods performed or applied at room temperature or for the adhesion of temperature-sensitive substrates.
The international patent application WO 99/58590 originating from the applicants of the present application themselves describes a substance system in the form of a one-component dispersion which comprises deactivated isocyanates and cross-links already at low temperatures, particularly at temperatures below 70xc2x0 C.
It is thus an object of the present invention to provide one-component dispersions which cross-link at lower temperatures.
It is also an object of the present invention to provide essentially aqueous one-component dispersions which, on the one hand, are storage-stable at room temperature in the dispersion state and, on the other hand, begin to cross-link during and/or after the removal of water (e.g. after application to a substrate).
In particular, an object of the present invention is to provide essentially aqueous one-component systems of surface-deactivated isocyanates and isocyanate-reactive polymers which may be stored in the dispersion state, but when applied as layers or films cross-link at low temperatures during and/or after removal of the water. Here, in particular, the substance system described in WO 99/58590 is to be developed further and optimized for its application.